The present invention concerns apparatus and a method for electronically compensating for the physical misalignment of a space fed microwave lens antenna. More particularly, it concerns apparatus and a method for accomplishing such correction in a space fed lens antenna deployed in outer space or other such remote or unattended location.
The cost of deploying very large phased array antennas has thus far favored reflector type antennas, regardless of application. When fielded, array antennas have tended to be unique installations that have cost up to ten thousand dollars per radiating element. New developments in solid state technology promise to change this condition as the production cost of a single chip transceiver and element approach the hundred-dollar level. This should result in a proliferation of large, agile beam solid state antennas in a number of interesting applications that require high gain, wide bandwidth, and electronic countermeasure (ECM) resistance.
The hundred-dollar transceiver is expected to contain a phase shifter, power amplifier, low noise amplifier, T/R switches, and a microprocessor. This technology advancement has the potential to support a very large, affordable, active aperture antenna with limited intelligence at the element level. However, the problem of distributing the rf energy to the antenna face is made more difficult as the array size increases. Feeding this antenna will be a major technical challenge.
When volume is not a prime concern, an attractive solution to the feeding problem is the space fed microwave lens. The size, weight and mechanical complexity of a constrained feed is avoided, and the "double transform" nature of the feed-lens combination affords the antenna designer a second level of control over the radiative properties of the system.
As long as scattering from support structures can be controlled, a small feed array can position an amplitude distribution on the rear face of the lens appropriate for producing a low sidelobe antenna pattern. By using a multibeam transform feed, the lens may be illuminated with overlapped subarrays that permit operation over a wide instantaneous bandwidth. Thus, the microwave lens has the potential to meet most of the advanced sensor requirements of future systems in radar and communications.
As the preceeding background suggests, the mechanical and electrical aspects of the feed array will affect the success of a space fed microwave lens. Control of deterministic and random feed errors will determine its ultimate rf performance. Predicting and understanding the effects of these errors is the first step toward controlling and, if necessary, actively compensating for them. For this reason a study was conducted to determine the effects of various feed errors upon the electromagnetic performance of a microwave lens antenna system.